1. Field of the Invention
This invention relates to a method and system for continuously measuring the volume of solid cuttings in a drilling mud discharged from a well during a rotary drilling operation and the volume of mud carried over with the cuttings during separation of the cuttings from the drilling mud utilizing a shale shaker.
2. Background of the Invention
As is well known, drilling fluids are employed when drilling holes into subterranean formations. The drilling fluid, usually referred to as drilling mud, consists of a mixture of liquids and solids to provide special properties to better perform the following primary functions in a drilling well. These functions are:
1. To lift the formation cuttings to the surface.
2. To control subsurface pressure.
3. To lubricate the drill string and bit.
4. To aid bottom-hole cleaning.
5. To provide an aid to formation evaluation.
6. To provide protection to formation productivity.
The drilling mud is circulated down the drill string, through the bit, and returns to the surface through the annular space between the drill string and the borehole wall. The drilled cuttings are picked up at the bit and returned to the surface for separation from the mud and for disposal. This removal of the drilled solids from the mud stream is critical to the subsequent reconditioning of the mud for recirculation in the well.
The hole-cleaning ability of the mud is a very important parameter. The buildup of cuttings in the annulus can contribute to, if not directly cause, pipe sticking and twist-offs. This is especially true when drilling a deviated well since a bed of cuttings is almost always formed on the lower side of the drill pipe. By measuring the cuttings discharge at the surface, the buildup of cuttings in the well can be detected early and remedial action taken to prevent a catastrophic failure.
The cuttings from the well are discharged over a shale shaker screen to separate them from the drilling mud. Some of the mud adheres to the cuttings and is carried over with the cuttings discharged from the shale shaker. This portion of mud is lost to the mud system, which has been reported to be as high as two barrels of mud for every barrel of cuttings.
This invention provides a continuous, quantitative method of determining the hole-cleaning ability of the mud under specific drilling conditions by measuring the volume of cuttings being discharged from the shale shaker and also measuring the mud loss due to carryover. The quantitative measurement of these parameters makes possible the determination of the optimum annular mud velocity and the rheology of the mud to obtain the maximum removal of cuttings from the well. These continuous, quantitative measurements are not now being made during drilling operations by any system in use today.